Fwd: IMPORTANT! Network is unreachable

Clifton Royston cliftonr at lava.net
Sat Aug 9 18:37:24 UTC 2008

On Sat, Aug 09, 2008 at 05:23:32PM +0400, KES wrote:
> 09.08.08, 16:22, "Matthew Seaman" <m.seaman at infracaninophile.co.uk>:
> > Andrew Snow wrote:
> > > Usually if there is more than IP in a given subnet on an interface, you 
> > > give it a /32 netmask.  Only the first IP in a subnet should have the 
> > > full netmask.
> > > 
> > > So your example should look like this:
> > > 
> > >     inet netmask 0xffffff00 broadcast
> > >     inet netmask 0xffffffff broadcast
> > /32 netmasks for 2nd and subsequent IP alias addresses used to be
> > mandatory and are arguably more correct, but nowadays you can use
> > the actual netmask for the network instead.  Was fixed a year or
> > two ago.  It's a wetware compatibility thing -- other unixoid OSes
> > never had the /32 netmask requirement, and it kept tripping people up
> > when swapping between OSes.
> > Unfortunately I can't say exactly what the problem the OP is experiencing
> > is due to, but the way routes are appearing and disappearing on a 5
> > minute timescale does suggest dynamic routing problems to me.  As a 
> > work-around, if the OP wanted to override the information routed gets
> > from the network, then he could use /etc/gateways to have the local
> > routed append some static routes to the routing table -- see routed(8)
> > for the gory  details.  Losing a route for a directly attached network
> > looks like a bug to me though.
> > >     inet netmask 0xffffff00 broadcast
> > >     inet netmask 0xffffffff broadcast
> /24 mask on each IPs on same interfaces is working fine on FreeBSD 6.3
> So I do not think that problem is with the network mask. Because of even ping
> returns network is unreachable! 
> Now when I upgraded to v7 I see trouble described earlier.
> So this is must be counted as BUG of v7

  I happened to see recently a report of a similar problem with 7.0 on
a private mailing list.  Again, there were multiple IP addresses
configured within the main subnet of the interface (this time
configured as /32s on other physical interfaces) and again, after a
while the system lost connectivity to its main subnet and "forgot" how
to ARP for addresses on the interface.  An important similarity - the
routing info like yours showed the attached network with the G flag, as
being reachable via the gateway address within the same subnet.

  I can't troubleshoot this, no access to the system in question, but I
thought it might help to know that others have run into the same

> The thing which is very interesting is:
> Why period is 5 min?

  Might be something to do with ARP?  Not sure.

  -- Clifton

    Clifton Royston  --  cliftonr at iandicomputing.com / cliftonr at lava.net
       President  - I and I Computing * http://www.iandicomputing.com/
 Custom programming, network design, systems and network consulting services

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